Oxidation of Acyclovir by a Cuprate(III) Periodate Complex in Aqueous Alkaline Media: A Kinetic and Mechanistic Approach

Abstract

The oxidation of acyclovir by diperiodatocuprate(III) in aqueous alkaline media, at a constant ionic strength of 0.01 mol⋅dm−3, was studied spectrophotometrically at 25 °C. The reaction between acyclovir and DPC in alkaline media exhibits 1:4 stoichiometry (acyclovir:diperiodatocuprate(III)). The main oxidation products were identified by a spot test, along with infrared and liquid chromatography mass spectral studies. The oxidation reaction is first order with regard to the diperiodatocuprate(III) concentration, but has less than unit order in the acyclovir concentration and negative fractional orders in the periodate and alkali concentrations. Intervention of free radicals was observed in the reaction. The oxidation reaction in alkaline media was shown to proceed via a diperiodatocuprate(III)–acyclovir complex, which decomposes slowly in a rate determining step followed by subsequent fast steps to give the products. A suitable mechanism is proposed for these observations. The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to the slow step of the mechanism, along with the thermodynamic quantities, were determined and discussed.